Abstract

Most existing brain-computer interfaces (BCIs) detect specific mental activity in
a so-called synchronous paradigm. Unlike synchronous systems which are operational at
specific system-defined periods, self-paced (asynchronous) interfaces have the advantage of
being operational at all times. The low-frequency asynchronous switch design (LF-ASD) is a
2-state self-paced BCI that detects the presence of a specific finger movement in the ongoing EEG.
Recent evaluations of the 2-state LF-ASD show an average true positive rate of 41% at the fixed false
positive rate of 1%. This paper proposes two designs for a 3-state self-paced BCI that is capable
of handling idle brain state. The two proposed designs aim at detecting right- and left-hand
extensions from the ongoing EEG. They are formed of two consecutive detectors. The first detects
the presence of a right- or a left-hand movement and the second classifies the detected movement
as a right or a left one. In an offline analysis of the EEG data collected from four able-bodied
individuals, the 3-state brain-computer interface shows a comparable performance with a 2-state
system and significant performance improvement if used as a 2-state BCI, that is, in detecting the
presence of a right- or a left-hand movement (regardless of the type of movement). It has an average
true positive rate of 37.5% and 42.8% (at false positives rate of 1%) in detecting right- and left-hand
extensions, respectively, in the context of a 3-state self-paced BCI and average detection rate
of 58.1% (at false positive rate of 1%) in the context of a 2-state self-paced BCI.